Seismic Performance of Grouped Helical Piles in Pinned and Fixed Connections

Abstract

Helical piles have yet to be nationally considered an acceptable foundation for structures in areas of high seismic activity. This remains despite evidence of helical pile survival stories from recent earthquakes where other foundations failed, and helical pile systems sustained minimal damage. This study investigates the seismic behavior of grouped helical piles to begin the process of their acceptance as viable foundations in these seismically active environments. A full-scale shake-table test program was conducted on individual and grouped helical piles in a dense sand medium. The shake table simulated base motions recorded from past earthquakes. This paper discusses analysis and results of the grouped helical pile-soil system’s performance characteristics when subjected to seismic loads. Additionally, comparisons are made between the two commonly used types of pile group connections: pinned and fixed. In summary, pinned connections revealed better performance under seismic loads when compared to fixed connections for grouped helical piles. The pinned connection demonstrated higher damping ratios, lower lateral deflections, and lower bending moments than fixed connections. Overall, the helical piles performed satisfactorily in seismic conditions and did not reveal any type of pile deformations following the five-day testing sequence.